Fuel sender wiring

RobHomewood · Post by **RobHomewood** » Sat Mar 29, 2014 11:49 pm

I wonder if anyone can help. I have just replaced the fuel sender unit (new unit from Holden) in my 39 14 DHC and cant get the gauge to work. I tested the setup a while back before I installed the unit (with a loose earth wire to the bumper) and it worked then so I am not sure what I have now done wrong. Any help suggestions would be appreciated.
There was no sender unit in the car when I bought it and some of the wiring was missing also. I added the power supply and earth from the regulator to the dash and corrected the connections to the gauge. I have added an earth to the sender unit as it seems it needs one. I have fitted it under one of the fixing screws for the unit and taken it through to a bolt on the chassis under the rear seat where a wire (from the trafficator I think) is already connected. I have no clues as to where the earth wire should be attached and there isn't one shown on the wiring diagram but there is an earth shown to the reserve fuel switch adjacent but I dont have any wiring to that either (it doesnt work) hence my new earth. But should I be earthing from via reserve unit (not that that unit has an obvious place to connect on mine anyway)? I cant see how that would be different. I even wonder whether I should reverse the conections because this is a positive earth system?
Symptoms: when all connected and I switch on ignition the gauge needle sweeps to max immediately (the tank is less than half full) I have been warned not to leave it on as I may burn out the gauge.
I'm hoping someone has wired one up and can see my mistake...............

deckell · Post by **deckell** » Sun Mar 30, 2014 3:54 am

Rob i had a frozen float on my p3 after freeing the float i had to get the float calibrated with the gauge or vice visa.it now works perfectly just a thought, may be you need to consider this option,then again it could be more along the lines that you wrote about. hoping you sort it soon please advise how you get on regards Derrick.Smith

RobHomewood · Post by **RobHomewood** » Sun Mar 30, 2014 9:34 am

Thanks Derrick. I dont think the float is stuck- the sender unit in brand new never been used and all I have done is replace the new short arm float with an original float with longer arm.Besides the gauge needle goes off the top of the scale and so fast I dont think it could just be reading 'full'.
There is only one obvious terminal on the sender unit and with a cork gasket it probably cannot make a circuit through the fuel tank even if the tank itself is effectively earthed. That is why I added the earth connection under one of the fixing screws but I am now doubting that this is correct. Any suggestions welcome

luli · Post by **luli** » Sun Mar 30, 2014 6:01 pm

On What position the reading is stuck - full or empty?
Also see this discussion:
http://www.rover-forum.thersr.co.uk/vie ... nder#p7888

RobHomewood · Post by **RobHomewood** » Sun Mar 30, 2014 11:26 pm

Hi Luli.
The gauge is not stuck in any position. When all connected up it shows empty until I switch on ignition then it immediately swings off the top of the scale. I have looked at your links before but didnt find anything on the location of any earthing/second wire to the sender unit/ tank or reserve unit. To see a photo of a fully wired up sender and reserve unit in situ would be most helpful
regards
Rob

luli · Post by **luli** » Mon Mar 31, 2014 6:55 am

What you see indicates an open circuit. Try this: take a conductor and short momenterily the live condutor at the sender (on the petrol tank) to the case of the sender. The guage indication should go th empty. If it does not, try to short it to a known good "ground". If it goes to empty there, then you have an ungrounded petrol tank, which is bad, even dangerous!
Some pictures you can see here: http://wp.me/pXLKy-1nt (provisional connection, for testing. Note the temporary ground wire).
Click on the images to enlarge.
Only a single wire (18, blue-purpule) is connected to the sender, according to the circuit diagram http://wp.me/pXLKy-St, Which means that the petrol tank itself must be grounded.

RobHomewood · Post by **RobHomewood** » Fri Apr 04, 2014 5:12 pm

Thanks Luli and Derrick for your input. Having tried various wiring alternatives to no avail I came to the conclusion that although the gauge had been working previously it was no longer! Fortunately I had a spare and once fitted this worked. Hurrah. However I then discovered that the oil level button just swung the needle to the max stop. I replaced the old wiring but no better. I have left the oil unit disconnected for the moment but the gauge still swings to the max stop when the button is pressed. A job for later...........

chris dancey · Post by **chris dancey** » Sun Apr 06, 2014 6:08 am

If you live near the Brighton area, I have a test rig that I made up to check gauges and sender units. My situation was that the dashboard gauge was faulty on the 10hp Coupe. I have sent both items to ' Speedy Cables ' for repair.

My testing of both the other 10s items proved they were working perfectly.

RobHomewood · Post by **RobHomewood** » Mon Apr 07, 2014 2:52 pm

Thanks for the offer Chris but I am way out on a limb down in Cornwall. I did obtain a spare secondhand oil level sender unit but it appears not to work either- the coil is soaked in oil which I guess is a common hazard. I may send this off for repair in due course but actually the new Holden 'Smiths' replacement unit is a good match visually so I may just get a side mount version of that (c. £45 or £53 plus VAT). Plenty of other issues to address first

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Fuel sender wiring

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